Melanogenesis-Inhibitory and Cytotoxic Activities of Triterpene Glycoside Constituents from the Bark of Albizia procera

Five oleanane-type triterpene glycosides including three new ones, proceraosides E–G (<b>1</b>–<b>3</b>), were isolated from a MeOH-soluble extract of Albizia procera bark. The structures of <b>1</b>–<b>3</b> were determined by use of NMR spectra, HRESIMS, and chemical methods. Compounds <b>1</b>–<b>5</b> exhibited inhibitory activities against the proliferation of the A549, SKBR3, AZ521, and HL60 human cancer cell lines (IC<sub>50</sub> 0.28–1.8 μM). Additionally, the apoptosis-inducing activity of compound <b>2</b> was evaluated by Hoechst 33342 staining and flow cytometry, while the effects of <b>2</b> on the activation of caspases-9, -8, and -3 in HL60 cells were revealed by Western blot analysis.